Acoustical Physics Quiz 3

Unit 2 Properties of Ultrasound Physics

Pulse Duration

From the beginning of a pulse to the end of the pulse. The actual time that there is a pulse.

Pulse duration units?

microseconds (μs)

Pulse duration typical values?

0.5 - 3.0 μs

Pulse duration formula?

PD = # cycles in pulse x period (μs)

PD = # cycles in pulse / frequency (MHz)

Pulse duration is determined by?

the sound source

Is pulse duration changed by the sonographer?

NO (PD)

Pulse duration is ____________ to the number of cycles in the pulse.

proportional

Pulse duration is ________ proportional to period & _________ proportional to frequency.

directly; inversely

Which type of pulse is more desirable in diagnositc imaging and why?

Short pulses because they give us a better image & have a greater accuracy.

Spatial Pulse Length (SPL)

The distance or length from the start to the end of one pulse.

Spatial pulse length units?

mm

Spatial pulse length typical values?

0.1 - 1 mm

Spatial pulse length formula?

SPL = the number of cycles x wavelength

Spatial pulse length determines?

longitudinal resolution (image quality)

Spatial pulse length is determined by?

sound source & medium

Can spatial pulse length be changed by the sonographer?

NO (SPL)

Spatial pulse length relationships:

Directly proportional to the number of cycles

Directly proportional to the wavelength

Inversely proportional to the frequency

There is a 3 MHz & 5 MHz transducers both with 5 cycles. Which will have the greatest spatial pulse length?

3 MHz

A lower frequency will have a longer wavelength. SPL & wavelength are directly proportional.

lower frequency = long wavelength = longer SPL

Pulse Repetition Period (PRP)

The time from the start of one pulse to the start of the next pulse

Pulse repetition period units?

units of time (typically μs)

Pulse repetition period typical values?

100 μs - 1 ms

Pulse repetition period is determined by?

sound source (PRP)

Can pulse repetition period be changed by the sonographer?

Yes by changing the depth (PRP)

Pulse repetition period is generally about __________ times longer than pulse duration.

100-1000

this is due to the listening time

If you’re imaging deep, your PRP is __________?

longer

If you’re imaging shallow, your PRP is _________?

shorter

Pulse Repetition Frequency (PRF)

The number of pulses sent out per second

Pulse repetition frequency units?

Hertz (Hz)

Pulse repetition frequency typical vlaues?

1-10 kHz (1,000-10,000 Hz)

Pulse repetition frequency is determined by?

sound source (PRF)

Can the pulse repetition frequency be changed by the sonographer?

Yes by adjusting the depth (PRF)

PRP & PRF relationship?

inversely related

They are reciprocals, meaning they multiply together to equal 1.

Pulse repetition period formula?

PRP (sec) = 1/PRF (Hz)

Pulse repetition frequency formula?

PRF (Hz) = 1/PRP (sec)

As imaging depth increases (going deeper), PRF _________?

decreases

As imaging depth decreases (shallower), PRF _________?

increases

When imaging shallow, our PRP is going to be _______, but our PRF will be _________

short; high

Which of these four values for PRF would have the longest PRP?

2 kHz

4,000 Hz

6 Hz

1 kHz

6 Hz

We want the longest PRP, so choose the shortest frequency.

Four pulses have PRP’s as listed below. Which of the following 4 waves has the highest PRF?

8 s

80 ms

5 ms

400 ks

5 ms

You want the lowest PRP to have the highest PRF.

Which of the following 4 pulses with the PRF’s listed below has the shortes PRP?

12 kHz

20 kHz

6000 Hz

1 kHz

20 kHz

You want the highest PRF to get the sortest PRP

Four waes have PRP’s as listed below. Which of the following four waves has the lowest PRF?

8 s

80 μs

800 ns

800 ms

8 sec

You want the highest PRP to get the lowest PRF

Duty Factor

The percentage or fraction of time that the system transmits sound; the time it talks/talking time.

Duty factor & PRF relationship?

directly related

(F&F go together)

If imaging shallow, duty factor will be?

high (DF)

If imaging deep, duty factor will be?

low (DF)

Duty factor formula?

Duty Factor (%) = Pulse duration (sec) / Pulse repetition period (sec)

Duty factor is determined by?

sound source (DF)

Can the duty factor be changed by the sonographer?

Yes by adjusting the imaging depth (DF)

Duty Factor typical values for pulsed?

0.1 - 1%

(less than one %)

Duty Factors typical values for continuous?

1.0 or 100%

Duty Factor is __________ related to imaging depth.

inversely

Adjusting the depth changes the PRP, which indriectly changes the duty factor.

If all other things remain constant, when the PRF increases the duty factor? (1)

increases (1)

(more pulses means the machine is talking more)

If all other things remain constant, when the imaging depth decreases (shallower) the duty factor? (2)

increases (2)

If all other things remian constant, when the pulse repetition period increases the duty factor? (3)

decreases (3)

(listening time increases so taling time decreases)

If all other things remain constant, when the pulse duration increases the duty factor? (4)

increases (4)

By adjusting the imaging depth, the operator changes?

1) Duty Factor

2) Pulse Repetition Frequency (PRF)

3) Pulse Repetition Period (PRP)

If all other factors remian unchanged, what happens to the duty factor when the PRF increases?

increases

decreases

remains the same

Increases

F & F go together

directly related

If all other factors remain unchanged, what happens to the duty factor when the imaging depth increases?

increases

decreases

remains the same

decreases

duty factor measures talking time & if we go deeper, the listening time increases

If all other factors remain unchanged, what happens to the duty factor when the PRP increases?

increases

decreases

remains the same

decreases

If PRP increases, duty factor will decrease becuase the listening time increases.

If all other factors remain unchanged, what happens to the duty factor when the sonographer uses a new transducer with a longer pulse duration?

increases

decreases

reamins the same

increases

longer pulse duration = larger pulse = talking more = duty factor increases

What is the duty factor if the pulse duration is 1 μs and the PRP is 1 ms?

100%

0.1'

0.01

0.001

0.001

Duty factor = PD/PRP

0.000001/0.001

Which of the following terms does not belong with the others?

A) increased depth of view

B) increased duty factor

C) increased PRP

D) decreased PRF

B

Duty factor is how much the machine is talking, so if we are going deeper we are talking less.

Determined by the sound source?

Pulse Duration, PRP, PRF, & Duty Foctor

Describes Shallow Imaging:

high PRF, short/low PRP, high duty factor, & less listening.

Describes Deep Imaging:

low PRF, long/high PRP, low duty factor, & more listening.

Resolution

The ability to image accurately

Longitudinal Resolution (axial resolution)

The ability to distinguish two structures that are close to each other FRONT to BACK, parallel to or along the main axis.

What does the accronym LARRD stand for?

Longitudinal Axial Range Radial Depth

The shorter the pulse, the _______ the LARRD resolution.

better

Axial resolution is determined by?

spatial pulse length (medium & sound source)

As frequency increases, the numerical value of axial resolution ____________*

decreases*

We have better LARRD resolution & higher quality images with?

high frequency transducers

LARRD resolution units?

mm

Can LARRD resolution be changed by the sonographer?*

NO*

LARRD resolution typical values?

0.05 - 0.5 mm

LARRD resolution formula?

LARRD (mm) = SPL/2

(the smaller the number, the better the picture quality)

For the best axial resolution we want?

less ringing & high frequencies

What stops the ringing?

dampening the crystal

What makes a pulse short?

Few cycles in the pulse

A pulse is short if each cycle in the pulse has a short?

wavelength

Shorter wavelengths are characteristic of?

higher frequency sound

Pulses made of higher frequency cycles have?

superior axial resolution

Which of the following transducers has the poorest axial resolution?

A) 1.7 MHz and 4 cycles/pulse

B) 2.6 MHz and 3 cycles/pulse

C) 1.7 MHz and 5 cycles/pulse

D) 2.6 MHz and 2 cycles/pulse

C

bad resolution = low frequency with the most cycles

Which of the following transducers has the best axial resolution?

A) 1.7 MHz and 4 cycles/pulse

B) 2.6 MHz and 3 cycles/pulse

C) 1.7 MHz and 5 cycles/pulse

D) 2.6 MHz and 2 cycles/pulse

D

high frequency with the fewest cycles = best picture

Transducers

Any device that converts one form of energy into another. (acoustic to kinetic)

Piezoelectric effect

Desribes the property of certian materials to create a voltage when pressure is applied or when the material is mechanically deformed.

Reverse piezoelectric effect

When piezoelectric materials deform or change shape when they have a voltage applied to them.

Piezoelectric/ferroelectric material

Any kind of material that can turn sound into electrical energy.

Natural piezoelectric material

quartz

Man made piezoelectric materials

barium titanate

lead metoniobate

lead titanate

Lead Zirocnate Titanate*

Other terms for lead zirconate titanate?

PZT, ceramic, active element, crystal

What does the transducer case do?

Protects the internal components & protects the patient from electrical shock

What does the transducer electrical shield do?

Prevents electrical noise from contaminating the electrical signal that is going to be used to create the image

What does the transducer acoustic insulator do?

It is made out of cork or rubber & it uncouples the internal components from the case

The PZT or active element is shaped like?

a coin

How thick is the PZT?

½ wavelength thick

What is the matching layer?

what is touching the patient

What is the purpose of the matching layer?

To reduce the impedance from the crystal to the skin; increases the efficiency of sound transfer between the active element & the body.

How thick is the matching layer?

¼ wavelength thick

Damping element/Backing material

A material that is bonded to the active element that acts to limit the “ringing” of the pulse.